Ion exchange technology specifically addressing removal of perchlorate (ClO4−) and nitrate (NO3−) from groundwater, drinking water, or process waste streams is a relatively recent art utilizing strong base anion (SBA) resins. Using SBA resins, anions in aqueous solution, such as perchlorate and nitrate, exchange with stoichiometrically equivalent amounts of exchangeable anions on the resin surface, such as chloride (Cl−) SBA resin technology is practiced as a single use, disposable resin process, or as a regenerable resin process. Single use processes typically employ perchlorate-selective resins such as Purolite A-530E and Rohm and Haas PWA2 for treating water streams containing relatively low concentrations (<1 mg/L) of perchlorate. Non-selective SBA resins, such as Purolite A-600, have been used effectively to treat higher concentrations of perchlorate. The single use approach requires periodic resin replacement and disposal, typically by incineration. The performance and economics of the single-use approach are limited by resin treatment capacity, factors that limit time on-line (channeling, fouling, plugging, bacterial growth, compaction, and agglomeration), resin cost, and incineration cost.
Regenerable SBA resin processes typically use non-selective resins and are regenerated by ion exchange with one molar (6%) or higher concentration salt (sodium chloride or potassium chloride) brine. Regeneration of SBA resins configured as conventional “lead-lag” ion exchange processes result in the production of large volumes of spent brine contaminated with perchlorate, nitrate, sulfate, and other anions. The Calgon Carbon ISEP Process, described in U.S. Pat. No. 6,066,257, is a pseudo-continuous, counter-current ion exchange and regeneration process that uses SBA resins that has been employed to remove perchlorate and nitrate from drinking water. The ISEP process was developed to reduce the amount of waste brine; however, typical waste generation rates are about 1% of the treated groundwater. Other ion exchange processes that use SBA resins, such as the Basin Water Process, described in U.S. Pat. No. 6,878,286, have been developed in an attempt to reduce spent brine to less than 0.5% of the treated water. Waste brine from regeneration is not acceptable to most wastewater treatment plants due to high salt, perchlorate, and/or nitrate content. Catalytic and biological waste brine treatment and reuse technologies have been developed, but they are expensive and have not been reduced to practice.
A novel regeneration approach for SBA resins has been developed using ferric chloride and hydrochloric acid (HCl) to generate the ferrate ion, as described in U.S. Pat. Nos. 6,448,299 and 6,385,396. This approach enables very efficient regeneration of some SBA resins, especially for difficult to remove anions such as perchlorate. However, the primary drawbacks of this approach are materials compatibility, high cost of regenerating solution, handling safety, and difficulty and cost of ferric chloride brine disposal or reuse of either tetrachloroferrate or brine types of waste.